Reversed-phase columns support pore size

Reversed-phase chromatography is perhaps the most widely used chromatographic method. It was first developed by Howard and Martin (1950) to separate fatty acids by using a polar eluent (mobile phase) and a nonpolar stationary phase that consisted of paraffin oil and octane. Today the stationary phase consists of a liquid that is chemically bonded to a support. For example, the column packings contain octadecylsilyl (Cig), octylsilyl (Cg), butylsilyl (C4), or propylsUyl (C3), which are bonded to silica supports having various pore sizes (e.g., 100, 300, and 500 A) and particle sizes (e.g., 5 and 10 pm). The extent of retention of a molecule depends on the number, size, and stereochemistry of its hydrophobic (e.g., alkyl) and hydrophilic (e.g., ionic) groups. 

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